PROJECT SUMMARY Chronic hepatitis B virus (HBV) infection is a significant global health problem because it substantially increases the risk for developing liver cirrhosis and hepatocellular carcinoma. Worldwide, more than 240 million people are chronically infected with HBV, and infection with this virus accounts for ~80% of all liver cancer. The human immune system can eliminate HBV from the liver, yet often fails to do so, especially in those who become infected at an early age. HBV persistence is due in part to immunoevasive tactics employed by the virus as well as host-driven immunosuppression of antiviral immune responses during chronic infection that serves to limit inflammation and immunopathology. Thus, therapeutic manipulation of the antiviral T cell response represents a promising method of treatment to cure the infection. However, the lack of suitable model systems in which to evaluate new immunotherapeutic approaches represents a critical barrier in the field. The overall goal of this proposal is to develop a new mouse model for HBV that unites the physiological relevancy of the human immune system with the convenience and reproducibility of genetically defined transgenic mice. Our general approach will be to combine well-characterized mouse models of HBV replication with a new strain of humanized mice whose immune systems can be efficiently reconstituted with T cells from HBV-infected patients. We will then test the hypothesis that engraftment of human immune cells in these mice will lead to an HBV-specific immune response in the liver, and that this response will reflect the disease status of the human donor. To evaluate our hypothesis, we will carry out two specific aims. First we will introduce HBV replication into the liver of a mouse strain that contains a number of knock-in gene-humanizations to improve the engraftment, differentiation, and maintenance of human hematopoietic populations in the animals. Second, we will engraft these mice with PBMC from acute-resolved and chronic HBV patients, and characterize how these immune cells traffic to the liver and respond to hepatocytes that produce HBV antigens. The intent of developing this model system is to provide new means for studying the human HBV immune responses in vivo. This will fill a critical unmet need, and we anticipate that this system will have wide application for both basic and translational HBV research to understand T cell functionality in chronic HBV infection, evaluate novel immunotherapeutic approaches, and identify determinants of HBV immunopathogenesis. Such analyses could have a substantial impact on the study and treatment of chronic liver infections in humans.